1. Field of the Invention
The present invention relates to a vapor deposition device for fabricating a compound semiconductor, and, in particular, to a vapor deposition device for fabricating a compound semiconductor wherein an organometallic gas for use in the formation of the next thin film can be immediately provided and supplied to a reaction furnace when different types of thin films are continuously propagated by metal organic chemical vapor deposition (MOCVD) using organic metals, and a constant flow can be normally maintained in the reaction furnace during film-forming so that a thin-film with good uniformity can be obtained.
2. Description of the Prior Art
FIG.1 is a general configuration drawing showing a conventional vapor deposition device for fabricating a compound semiconductor.
In the drawing, the conventional vapor deposition device for fabricating a compound semiconductor comprises a reaction furnace 131; a plurality of bubbler vessels 101 to 105 for storing organic metals used to form various types of films; a plurality of mass flow controllers 111 to 115 for controlling the flow of a carrier gas (for example hydrogen H.sub.2) at a specified rate to the primary side of the bubbler vessels 101 to 105; a mass flow controller 116 (for supplying the carrier gas H.sub.2) for controlling the flow of the carrier gas H.sub.2 for flow compensation; and a plurality of valves 121 to 125 as part of an organometallic gas supply line for forming various films, connected to the secondary side of the bubbler vessels and to the mass flow controller 116.
The operations of the plurality of valves 121 to 125, the mass flow controller 116, and the mass flow controllers 111 to 115 are controlled by a process control unit 150 such as a microcomputer system.
During the formation of a thin-film of a semiconductor, a specified organometallic gas is supplied to the valves 121 to 125 from the secondary side of the bubbler vessels 101 to 105. A plurality of types of synthesized organometallic gases is supplied to the reaction furnace 131 by opening and closing the valves 121 to 125, and the thin film of the semiconductor is formed. For example, when an InGaP thin-film is formed, organic metals TMI (TriMethyl Indium) and TMG (TriMethyl Gallium) are supplied to the reaction furnace 131 through a PH.sub.3 (phosphine) and AsH.sub.3 (arsine) line 141 and the film is formed by the metal organic chemical vapor deposition (MOCVD) method.
A multilayer thin-film semiconductor device such as an LED and the like is formed by the MOCVD method with a semiconductor laser for a compound semiconductor (in this case a substrate is a GaAs substrate).
When a multilayer thin-film of a semiconductor is formed by means of a conventional vapor deposition device for fabricating a compound semiconductor, after a certain layer is formed the next film-forming organometallic gas is fed to the reaction furnace 131 by opening and closing the valves 121 to 125 under the control of the process control unit 150.
When the valves are opened the flow to the reaction furnace 131 suddenly becomes excessive and a time delay occurs before the flow rate is stabilized to the specified amount, therefore the uniformity of thickness of the resulting film of a semiconductor is poor.
Also, the total flow within the reaction furnace 131 must normally be uniform during the formation of the thin-film in order for the inner pressure of the reaction furnace 131 to be normally uniform.
Specifically, when the inner pressure of the reaction furnace 131 is not uniform, the formed thin-film lacks uniformity because of variations in the inner pressure.
Therefore, when a certain layer of film is formed the organometallic gas is supplied at a specified flow rate and, in the case where the specified total flow is not provided within the reaction furnace 131, a necessary amount of carrier gas is supplied by the mass flow controller 116 to compensate for the flow rate.
However, when the specified flow rate of the organometallic gas differs from a flow rate at the total film-forming time, the flow rate of the carrier gas H.sub.2 for flow compensation must also be changed.
When the flow rate in the mass flow controller 126 is changed there is a time delay until the value of the change is stable, therefore there is also a time delay until the inner pressure of the reaction furnace 131 is stabilized, therefore the uniformity of the formed film is poor.
In addition, because of the time delay before the amount of the above-mentioned organometallic gas supplied and the flow rate of the carrier gas for flow compensation reach uniform values, the formed films in a semiconductor is poor and the characteristics of the formed semiconductor are poor.
As outlined above, with a conventional vapor deposition device for fabricating a compound semiconductor:
(1) When the valves 121 to 125 are opened, the flow to the reaction furnace 131 suddenly becomes excessive and a time delay occurs before the flow rate is stabilized to the specified amount, therefore the uniformity of the thickness of the resulting film is poor.
(2) When there is a flow rate change in the mass flow controller which provides flow rate compensation, there is a time delay until the value of the change is stable, therefore a time delay is produced until the inner pressure of the reaction furnace becomes stable and the uniformity of the formed film is poor.
(3) Because there is a time delay before the amount of the above-mentioned organometallic gas supplied and the flow rate of the carrier gas for flow compensation reach a uniform flow value, the formed films is poor and the characteristics of the formed semiconductor are poor.